1. Field of the Invention
The present invention relates to band-sawing machines which are intended to be employed for sawing metal parts such as metal bars or the like.
2. Description of the Prior Art
In the case of horizontal band-saws, these machines have a movable work unit placed above the intended location of the workpiece to be sawn, said unit being constituted by the band as well as its drive mechanism. Penetration of the band takes place by vertical displacement of the work unit under the action of its weight alone. However, this movement, which determines the rate of penetration of the band, is braked by a hydraulic device having a leakage circuit provided with a flow-rate regulator.
As a general rule, machines of this type are provided with safety systems having the function of stopping their operation in the event of overload or of failure of the band. Thus French patent No. 2,556,258 describes a sawing machine in which a feeler is placed in contact with the back of the saw-band and which is capable of producing action on a device for initiating stoppage of downward motion of the movable work unit in the event that the force applied to said feeler exceeds a predetermined threshold value. In addition, provision is made between said feeler and the device controlled by this latter for an intermediate element which is capable of producing a modification of the conditions of action of the feeler on the member for stopping the movable work unit as a function of the width of the part to be sawn.
However, this does not make it possible to obtain a sufficient degree of operational safety of sawing machines of the type considered. It is in fact necessary to ensure that the cutting force never exceeds both the possibilities of mechanical resistance of the saw-band body and the possibilities of frictional drive of said saw-band. In point of fact, when many teeth of the band are engaged, this results in an increase in the resistance set up in opposition to the band drive, which is in turn liable to produce rapid degradation and failure of the band.
In order to overcome this drawback, it has already been proposed to equip sawing machines of this type with an electronic regulating device for adjusting the rate of travel of the band as a function of the stresses sustained by this latter. However, a device of this type is particularly complex and costly as well as inconvenient to use.
It is for this reason that the present invention is directed to a sawing machine having a regulating system of very simple design which is capable of automatically ensuring satisfactory operational safety in the event of increase in the resistance set up in opposition to the saw-band drive.